Process of treating armor-plates.



A. FQMITGHBLL & W. H. JONES.

PROCESS OP TREATING ARMOR PLATES. APPLIQAMON ITILBD., 1111111.24. 19m.

19.1 00,1913, Patented June 16, 1914.

'2 SHEETS-SHEET l.

@Hou/miga A. P. MITCHELL & v'WQ H. JQNBS.

PROCESS OF TRBATING ARMOR PLATES.

APPLICATION FILED MAR-,24,191.0l

1,100,193, Patented June 16,1914,

2 SHBETS-SHEET 2.

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staats PATENT oEEIoE.

ANDREW E. MITCHELL, or PITTSBURGH, AND WILLIAM II. JoNEs, 0F MUNHALL, PENNSYLVANIA, AssIeNoEs To CARNEGIE STEEL COMPANY, oF PITTSBURGH, PENNSYLVANIA, A coRPoEaTIoN or NEW JERSEY.

PRGCESS 0F TREATING ARMOR-PLATES.

Linares.

Specification of Letters' Patent. I P'\,te11tedJ1111e 16, 1914.

Application led March 24, 1910. Serial No. 551,297. 4

To all whom t may concern:

Be it known that we, ANDREW l?. MITCH- ELL, a. citizen of the United States, residing at Pittsburgh, Allegheny county, Pennsylvania, and VILLIAII H. JONES, a citizen ot the United States, residing at Munhall, in the county of Allegheny and IState 01"' Pennsylvania, have invented. certain new and useful Improvements in Processes ot rl`reating Armor-Plates; and we do declare the following to be a full, clear, and exact description of the invention, such as will enable others skilled in the art to which it appertains to make and use the same.

`Our invention relates tothe treatment of steel and alloy steel after being formed Ainto plates and similar articles.

@ne object of our invention is to provide a novel process of treating steel and alloy steel plates, in which the plates are tirst supercarburized to a greater depth than is possible in existing processes and the over carburized portions are then decarburized preliminary to hardening whereby the hardened plates will have a stratum of glass hard steel of greater depth than has heretotore been possible, and whereby the coarse crystalline structure of such hardened steel is eliminated or greatly reduced, and when desired,is covered with a thin outer layer of decarburized and relatively soft steel.

Referring to the accompanying drawings forming part ot this specification, Figure l is a diagram showing graphically the diit'erence in the carbon content of the steel at yvarious depths trom the outer surface thereof ina supercarburiied plate whichv has been decarburized low in accordance with our Invention. Fig. 2 is a similar d1a-.

gram showing in like manner a supercar burized plate at'ter being decarbu-rized to a medium depth in accordance with our vention. Fig. 3 is a similar illustration ot' a homogeneous plat-e after having been decarburized. Fig. il is a transverse section ot a plate showing the structure ot' the steel when in a fibrous condition. Fig. 5 is a similar section showing the structure after deep supercarbiuization andprior to water hardening, and plainly indicating' the coarse crystalline structure adjacent tothe tace4 Is`a section similar to `that shown in figs. 4 and 5 and showing the structure of the plate ot Fig. 5 after the water 'hardening operation. Fig. 7 is a section similar to thatin Figs. at, 5 and G showing the plate at'ter being -decarburized and water hardened, and showing plainly the tine tool steel chill resulting'from the decarbnrizing step of our process.

At the present time, steel plates contain a certain percentage of carbon, and various e alloys are employed to make alloy steel plates. Such plates are .supercarburized so as to obtain about 1.2 per cent. of carbon on the surface, the carbon content gradually decreasing from the face inward until at a depth of one-half inch from the Surface the plate contains from .5 per cent. to .9 'per cent. of carbon, or a carboncontent enabling the plate to -take on a glass hardness after hardening to a depth ot' not exceeding threefourths of an inch from the surface. It is conceded by those familiar with the manufacture of such supercarburized plates that the glass-hardenedportion oit' the plate is the most essential for some purposes, such as in making armor, as in such case its purpose is to destroy the point ot' the projectile and keep it from penetrating the remaining portion. Such carbin'ization and depth of glass hardness, however, Ahas heretot'ote been limited von account of over supercarbnrit/iinf, which causes a portion thereof to have. a very coarse crystalline structure atter hardening. This condition is detrin'iental by rcason of having practically no elastic ,limit and being. very low in tensile strength, 'so that when subjected to the impact ot' a' projectile, the hardened face. breaks up and flakes oit around the point ot impact instead o't `holding together and more et'- vtectively resisting vthe projectile.

ln decarburizing. steel and alloy steel plates in accordance with our process we take platesv of almost any composition, preferably containing not over 0.5 per cent. ot carbon, and snpercarburize such, plates by any ot theseveral known methods until at the surface the carburiaed plates lia-ve,A about 1.5 per cent. carbon, and, .at a depthf ofv one and one-halt inches from' the suriace, contain about .5 per cent. carbon. j Having secured the desired carbon content. at the 'redown to a specilied depth depending on the4 length of time the plate is maintained at the decarburizing temperature. 4 There are various ways in which the decarburizing oper-- ation may be effected and different decarl'burizing agents and various temperatures may be used to produce the same effect, the best results in the shortest time known to us at this time being obtained by arranging the plates with the surfaces to be decal'- burizednext to a bed of silica sand or finely ground iron ore, and heating the same to a temperature of approximately 1025 degrees centigrade for a specified length of time.

'To reduce the over supercarburized portion of the plate so as to obtain from .70 to .90 per cent. carbon at the highest point, a medium hardness cannot be retained next to the surfaceA but the surface will be very soft,

or contain from .10 to `.18 per cent. carbon. To get this surface back to a carbon of say .45 to .8 0 per cent. it becomes necessary to recarburize the plate. by covering ity with a carbonaceous material during the hea-ting for reforging, or by the same heat treatment 'in case the plate is not to be reforged.

To more fully illustrate the state or conditionof the four plates illustrated' in the.

drawings after having been treated inaccordanee with the steps of our process, assume the vertical lines A, B, C, D, E, F, Src.l to indicate the amounts or percentages of carbon present, and thehorizontal lines, a, b, c, d, e, f, &c., to indicate diiferent depths or distances in inches and fractional parts of an inch inward from the face or surface of the plates.

Referring to Fig. 1 which represents a' plate which has first been supercarburized and then decarburivzed low, there is approximately .10 per cent. of carbon present at the surface; between .30 and .40 per cent. at b or at a depth of of an inch from the surfa'ce; .60 per cent. at c; .80 per cent. at d, between. .80 and .90 per cent at e; between .70 and .80 per cent. at f; .60 per'cent. 'at g; .50 per cent ath; between .50 and .40 per cent. from h'to j; and from .40 to .5 0 per cent. from j to n, depending on the carbon in theringot from which the plate ismade.

From 'the above, it is obviousthat the. .plate shown in Fig.' 1 is very soft at its sur- ;face but increases in hardness from a to e Vwhere it is extremely hard, then gradually' decreases in hardness from e to y', but still' retaining a glasshardness and decreasing in hardness, according to the amount of chill required from j to a point below.

Referring to Fig. 2 which represents a plate which has been supercarburized and then decarburized to a medium depth, it will be seen that there is .40 per cent. of carbon present at the surface and that the carbon content gradually increases from the surface to c, where it is highest, then decreases from e to y', and from j to n has the same carbon content.l The line of hardness will follow the line'of carbon to j and then decrease in hardness according to the amount of chill required.

Referring to Fig. 3 which illustratesa homogeneousplate which has been decarburized only, the same gradually increases in the amount of carbon present and in hardness from the surface to f. From f to n has the same carbon content but the line of hardness will extend to a point below f, ac`

cording tothe amount of chill required in hardening. y

From the above description of a decal*- burized plate, it will readily be seen some of the advantages of this process are, by reason of not having a high supercarburized face, namely; less liability of cracking and spalling or flaking od in manufacture, can -be more readily machined and when the plates are employedin making armor plates on account of having a greater depth of glass hardness and tool steel face after hardening,

such armor plates will be better fitted to re- -sist the projectiles and will withstand a higher velocityl than under the present processes, thus permitting the useof lighter armor having the resistance of plates of. heavier gage. The variations in the content of carbon, and depth to which the glass hardness and chill effect extends as herein disclosed are -to be regarded merely as approximations, which will vary depending upon the method of carburizing, and decarburizing agents employed and furnaces used in carrying out the process.

Having thus described our invention, whatwe claim is 1. A process of treating steel and alloy steel plates containing a high percentage of carbon on one surface which gradually diminishes from said surface, which consists in decarburizing said platev until the carbon in said surface is lowered and a stratum of soft steel formed on said surface, with a stratum of steel of tine chilled effect formed under said soft steel. n

2. A process of treating steel and alloy steel plates which consists in deeply super- -carburizing a plate until a coarse crystalline structure is formed at its surface, and then decarburizing the surface to a point sufficient to -cause it to retain a certain hard-r ness when the plate is hardened.

'3. The method of treating steel consisting in supercarburizing one face thereof," then deea-rburizing decrementally the Supercarburzed face and then heating and Water set ouil hands n presence of tWo subscribing quenehing the sii-treated steel. Witnesses. 4 .4. The method of treating steel consisting ANDREW F. MITCHELL. in supercarhurizing one side thereof, andA VILLIAM H. JONES. i then decrementally deearburizing the super- Witnesses:

earburized face of the steel. J .-VV. KISTLER,

In testimony whereof We have hereunto JOS.S. STEWART. 

